There are many systems in which redundant digital signals are provided, primarily for safety reasons. For example, in aircraft, the control surfaces are usually moved by servo motors in turn controlled by command signals generated in response to the pilot's movement of the pitch, roll and yaw controls in the cockpit. Thus, when the pilot pulls back on the pitch controller to operate the aircraft tail elevators, this movement might be sensed by four individual sensors to provide four redundant signals. This set of signals is then read into a processor which must, through software control, perform a signal selection logic to provide a preferred signal from the redundant signals as the actual command signal. Second and third groups each comprising a given number of redundant signals for different operations such as roll control, yaw control, etc. similarly require processing, the actual signal selection logic portion constituting a repetitive operation.
The basic disadvantage of the foregoing arrangement in the example of aircraft is the amount of processor time that is required to perform the signal selection. It would be far more advantageous to provide a special purpose device for use in such redundant systems for selecting one of the redundant signals prior to actual processing by the main digital processor equipment on the aircraft or even after processing of the signals. The primary advantage would be the reduction in the computation load of the main digital processore.
It should be understood that such a device would not be limited to use in aircraft control systems but would have application in any system wherein groups each made up of sets of redundant signals are provided and wherein it is necessary to select a preferred one of the redundant signals in each group for subsequent operations.